That's like saying, "In a world with cocaine, why do you need Red Bull?"
___
The only thing worse than diet soda is kombucha. And I'm not just saying that, because the artificial sweeteners in diet sodas give me migraines.
Though, I do wish diet soda did not exist. I now no longer order soft drinks at restaurants, because too many instances of people giving me diet when I wanted/needed regular soda. Worst was getting a diet coke at an airport...nothing screams, "PAIN!" like a migraine on a fucking airplane.